In the field of pipeline construction, particularly in the production of oil and gas, it is often necessary to construct and install a pipeline on the bottom of a body of water such as a sea bed, lake bed or ocean floor. Typically these pipelines are buried in a trench cut into the water bottom. Divers are typically employed to use various tools and devices to create a trench on the water bottom to bury the pipe line.
Efforts have been made to provide tools to assist divers in burying a pipeline and to facilitate the formation of the trench and burying the pipeline. One such device is that described in U.S. Pat. No. 5,288,172 to Reuhl. The Reuhl device incorporates two opposing water jet legs carried on a hydraulically powered carriage forward of venturi tubes. Within the water jet legs are a plurality of nozzles mounted in a rotating tube to deliver jets of water in different angular directions upon the water bottom to loosen sediment for removal through the venturi tubes. The disadvantages of this device are its size and its complicated mechanical system which requires frequent maintenance.
Another underwater pipeline trench-filling device is that described in U.S. Pat. No. 5,659,983 to Coutarel, et al. This device incorporates nozzles mounted on a pair of arms. In operation, the arms straddle the pipeline and trench to allow the nozzles to direct jets of water onto the sea bed adjacent to the trench to move loosened soil into the trench to cover the pipeline. The disadvantages of this device are that it must be used in conjunction with a trenching device and must be housed on some conveying means to move the opposing arms along the pipeline.
Another device for burying pipeline has been described and illustrated in U.S. Pat. No. 4,992,000 to Doleshal. This patent discloses an underwater trenching system that provides a trenching sled having high pressure water jets for digging and a vacuum head and lines for sucking the resulting sediment into a surge tank on a barge, from which it is re-deposited by a bury sled. A disadvantage of this device is that the device is large and difficult to use and incorporates high pressure vacuum pumps which are subject to frequent maintenance and unwieldy vacuum lines which may be difficult to manipulate.
Another device used to entrench and bury underwater pipeline is that disclosed in U.S. Pat. No. 4,389,139 to Norman. The Norman patent discloses a self-propelled apparatus having oscillating water jet nozzles used to cut away the water bottom formation to form a trench. The nozzles are positioned within the trench it creates as the device moves along the pipeline. One disadvantage of this device is that it is large and bulky making it difficult to manipulate underwater. Another disadvantage is that its many components make it subject to frequent maintenance and repair.
Consequently, a need exist for an improved apparatus to bury underwater pipelines that is simple to operate, easily to manipulate underwater, and that has minimal maintenance requirements.